1. Field of the Invention
The present invention generally relates to electrical connections formed on the exterior of semiconductor integrated circuit die structures and more particularly to an improved connection which eliminates the corrosion of exposed copper wiring on the die.
2. Description of the Related Art
Electrical connections are formed along the exterior of an integrated circuit die to permit access to the logic circuitry contained within the die. Wirebonds, typically formed from gold wire, are conventionally used to connect the last layer of metal on the integrated circuit die to the exterior environment. Typically, the last layer of metal within a high performance integrated circuit is copper.
However, copper is not a self-passivating metal and easily corrodes when left exposed. Therefore, it is conventionally necessary to form protective pads or other permanent conductive features over the copper wiring to prevent corrosions of the exposed copper. These pads are typically made of a less corrosion susceptible or self-passivating material such as tungsten, titanium, tantalum, aluminum, etc. The inclusion of protective pads in the structure is undesirable because of the additional materials, processing steps, and manufacturing complexity which potentially decrease die yield.
The invention described below overcomes the problems of conventional structures and processes by employing a structure and process that protects the copper wiring from exposure until just before the wirebond (or other electrical connection) is formed. This eliminates the need for additional structures such as conductive pads, yet still protects the copper from corrosion.
It is therefore, an object of the present invention to provide a method for forming a wirebond connection to an integrated circuit structure. The method includes forming an insulative, protective structure overlaying a corrosion susceptible metal wiring layer within the integrated circuit structure, defining a via partially through the thickness of the insulative structure above a portion of the corrosion susceptible metal without exposing the portion of the metal, and applying a conductive material to the portion of the corrosion susceptible metal. The attaching process included a preliminary process of at least partially exposing the portion of the corrosion susceptible metal. The conductive material completely covers the portion of the corrosion susceptible metal.
The invention removes a remaining portion of the insulative structure to expose the portion of the corrosion susceptible metal. This is performed through etching, laser ablation, or physically contacting the wirebond material against a remaining portion of the insulative material to expose the portion of the corrosion susceptible metal where the conductive material is applied to the corrosion susceptible metal using a heated capillary. In a preferred embodiment the conductive connection is a gold wirebond, and the corrosion susceptible metal wiring is copper. This process prevents the corrosion susceptible metal wiring from being exposed.
In another embodiment, the method includes forming an insulative structure overlaying a corrosion susceptible metal wiring within the integrated circuit structure, defining a via through the insulative structure above a portion of the corrosion susceptible metal, forming a protective barrier in the via, and applying a conductive material to the portion of the corrosion susceptible metal. The applying process includes a preliminary process of at least partially exposing the portion of the corrosion susceptible metal and completely covering the portion of the corrosion susceptible metal.
In another embodiment the invention includes defining a via through an exterior of the integrated circuit structure above a portion of the conductor, without exposing the portion of the conductor and applying a conductive material to the portion of the conductor. Once again, the attaching process includes a preliminary process of exposing at least part of the portion of the conductor.